<?php
include 'connect/connect.php';
$result = mysql_query('SELECT * FROM tbl_giangvien');

$s = '<option value=0 selected>Chưa sắp lớp</option>
';
while ($row = mysql_fetch_array($result)) {
  $s = $s . '
<option value=' . $row['id'] . '>' . $row['f_hovaten'] . '</option>
';
}

echo '<select name="f_giangvien">' . $s . '</select>';
?>